1. Field of the Invention
This invention relates to a tetrahydrobenzimidazole derivative represented by formula (I) shown below or a pharmaceutically acceptable salt thereof which are useful as a 5-HT.sub.3 -receptor antagonist ##STR2## wherein Het represents a heterocyclic group which may be substituted with 1 to 3 substituents selected from the group consisting of a lower alkyl group, a lower alkenyl group, a lower alkynyl group, a cycloalkyl-lower alkyl group, an aralkyl group, a lower alkoxy group, a nitro group, a hydroxyl group, a lower alkoxycarbonyl group, and a halogen atom; and X represents a single bond or --NH-- which is bonded to the carbon atom or nitrogen atom of the heterocyclic group.
2. Description of the Related Art
Conventionally known antagonists to 5-HT.sub.3 -receptors include azabicyclo compounds as disclosed in British Patents 2,125,398, 2,166,726, 2,166,727, and 2,126,728 (corresponding to JP-A-59-36675 and JP-A-59-67284, the term "JP-A" as used herein means an "unexamined published Japanese patent application"), tetrahydrocarbazole compounds as disclosed in British Patent 2,153,821 (corresponding to JP-A-60-214784), and azabicyclo compounds as disclosed in EP 280,444 (corresponding to JP-A-61-275276).